The present invention relates to a hydraulic pump, of the type having an output which is speed dependent up to a limiting value, and wherein beyond the limiting value, the output remains substantially constant irrespective of the speed.
Pumps having the above characteristics may be designed and constructed as rotary vane pumps, with the eccentricity of the rotor and the stator being adjustable in response to the load. However, in many cases, the additional structural requirements associated with pumps of the above type are not economically justified. Accordingly, it is an object of the present invention to provide a hydraulic pump having the described characteristics and which includes a rigidly constructed pump structure, and wherein the controlling action results from its design and does not require additional mechanical means.
Pumps having the above characteristics are commonly used as the lubricating oil pump for the internal combustion engine of an automobile, and where the speed of the engine and thus the rotary speed of the pump constantly changes. As is well known, the output pressure of such a pump is low when the engine speed is low, and as the speed of the engine increases, the output pressure of the pump also increases until a predetermined pressure value is reached. Pumps for this use commonly have a pressure relief valve which opens and diverts a portion of the pump output through a throttle and to a sump when the predetermined pressure value is reached, which of course represents a waste of energy. It is accordingly another object of the present invention to provide a hydraulic pump of the described type and which is energy efficient at high operating speeds.